In the manufacture of an electronic device such as a semiconductor device, it may be required to etch one of two regions made of different materials selectively against the other. For example, it may be needed to etch a first region made of silicon nitride selectively against a second region made of silicon oxide.
Generally, in order to etch the first region made of the silicon nitride selectively against the second region made of the silicon oxide, plasma etching using a hydrofluorocarbon gas is performed. In the plasma etching using the hydrofluorocarbon gas, the first region is etched by active species in plasma while the second region is protected by a deposit of fluorocarbon. This plasma etching is described in Patent Document 1.
Patent Document 1: Japanese Patent Laid-open Publication No. 2003-229418
To etch the first region made of the silicon nitride selectively against the second region made of the silicon oxide, however, a selectivity higher than a selectivity in the plasma etching using the hydrofluorocarbon gas is needed.
Furthermore, in the plasma etching using the hydrofluorocarbon gas, the second region is protected by using the deposit as stated above. If, however, a narrow opening is formed as the etching of the first region progresses, the opening may be clogged with the corresponding deposit, so that the etching of the first region is stopped.
In view of the foregoing, when etching the first region made of the silicon nitride selectively against the second region made of the silicon oxide, it is required to suppress generation of the deposit and acquire the high selectivity.